A suspension damper on a motor vehicle, commonly referred to as a shock absorber, reduces the amplitude of resilient suspension excursions between a sprung mass and an unsprung mass of the motor vehicle by converting into work a fraction of the kinetic energy of the sprung mass. Typically, a suspension damper includes a fluid-fill ed cylinder tube connected to the unsprung mass, a piston in the cylinder tube connected by a rod to the sprung mass, and valves on the piston which throttle fluid flow across piston during compression and rebound strokes of the suspension damper attributable to relative suspension excursions between the sprung and unsprung masses. In a twin-tube suspension damper, fluid in the cylinder tube displaced by the o connecting rod during a compression stroke of the suspension damper flows through a base valve to an annular reservoir around the cylinder tube and returns through the base valve during a rebound stroke of the suspension damper. In a monotube suspension damper, the volume of a gas chamber at an end of the cylinder tube opposite the connecting rod decreases and increases, respectively, during compression and rebound strokes of the suspension damper as the connecting rod enters and withdraws from the cylinder tube. A twin-tube suspension damper is adapted for pneumatic load leveling by the addition of an expansible chamber between the cylinder tube and the connecting rod which, when inflated with gas at elevated pressure, constitutes a pneumatic spring between the sprung and the unsprung masses. It has been proposed to equip a twin-tube suspension damper adapted for pneumatic load leveling with an external valve which reduces the stiffness of the suspension damper by shunting fluid directly from the cylinder tube to the annular reservoir as the pneumatic pressure in the expansible chamber decreases so that the stiffness of the suspension damper is maximum when the expansible chamber is inflated and minimum when the expansible chamber is exhausted to atmospheric pressure. The external valve, however, increases the size of the suspension damper and may be susceptible to damage from road hazards.